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\title{\huge GPG\normalsize}
\author{Josef ``Jeff'' Sipek $<$jeffpc@josefsipek.net$>$}
\date{}
\twocolumn
\begin{document}
\maketitle
\vspace{0.75cm}

\noindent\fbox{
\begin{minipage}{0.9\linewidth}
{\bf Cryptography}, n.

The science which studies methods for encoding messages so
that they can be read only by a person who knows the
secret information required for decoding, called the key
\end{minipage}
}


\section{History}
\begin{itemize}
	\item Caesar cipher -- used by Julius Caesar to deliver messages to
	his generals. A simple substitution cipher which relied on the
	illiteracy of majority of people.
	\item ROT13 -- ``modern'' version of the Caesar cipher. It shifts
	all characters by 13 instead of 3. Since there are only 26 letters
	in the english alphabet, an interesting effect occurs: encryption
	and decryption are one and the same operation!
\end{itemize}

\subsection{Symmetric ciphers}
Both Caesar and ROT13 are \emph{symmetric} ciphers. That means that the same
key is used during both encryption and decryption.

Some modern symmetric ciphers include \emph{AES} and \emph{Blowfish}. Both
of these ciphers, with a good key are \emph{effectively} unbreakable with
today's technology \& mathematics.

The only problem with symmetric ciphers is the fact that the key has to be
agreed upon over a secure channel -- in-person meeting, trusted courier, etc.


\section{Asymmetric ciphers}
The solution to the problem is ``simple'' --- it is called \emph{asymetric}
ciphers. Asymmetric ciphers consist of 2 keys. One \emph{private} and the
other \emph{public}. The public key is exactly that, public. You can post it
on your website and not worry about a thing. The private key should be kept
secure at all times. The private key allows you to do all the cool things.
:)

\subsection{Generating a key-pair}
Large random numbers are the basis of modern cryptography.

\noindent
\begin{minipage}{0.5\linewidth}
\begin{center}
\epsfig{file=Public_key_making.eps, scale=0.45}
\end{center}
\end{minipage}

\newpage
\subsection{Uses}
Such key-pair can be used to:
\begin{itemize}
	\item Sign/Verify signature
	\begin{itemize}
		\item Sign with private key
		\item Verify with public key
	\end{itemize}
\end{itemize}

\noindent
\begin{minipage}{0.5\linewidth}
\begin{center}
\epsfig{file=Public_key_signing.eps, scale=0.45}
\end{center}
\end{minipage}

\begin{itemize}
	\item Encrypt/Decrypt
	\begin{itemize}
		\item Encrypt with public key
		\item Decrypt with private key
	\end{itemize}
\end{itemize}

\noindent
\begin{minipage}{0.5\linewidth}
\begin{center}
\epsfig{file=Public_key_encryption.eps, scale=0.45}
\end{center}
\end{minipage}

\section{GPG commands}
\noindent{\bf Generate a new key-pair}:\\
\noindent{\texttt gpg --gen-key}\\

\noindent{\bf Sign a file}:\\
\noindent{\texttt gpg --clearsign \emph{filename}}\\
\noindent{\texttt gpg -a --sign \emph{filename}}\\

\noindent{\bf Verify a signature on a file}:\\
\noindent{\texttt gpg --verify \emph{filename}}\\

\noindent{\bf Encrypt a file}:\\
\noindent{\texttt gpg --encrypt \emph{filename}}\\
\noindent{\texttt gpg -a --encrypt \emph{filename}}\\

\noindent{\bf Decrypt a file}:\\
\noindent{\texttt gpg --decrypt \emph{filename}}\\

\subsection{Nasty, eh?}
Since using GPG directly is rather nasty, people have developed many
GUI/console frontends, as well as integrated GPG functionality right into
their applications. For example, Kmail, mutt, both integrate with GPG very
nicely.

\section{Resources}
Images shamelessly stolen from Wikipedia.

\begin{itemize}
	\item Wikipedia \\
		\url{http://en.wikipedia.org/wiki/Asymmetric_key_algorithm}
	\item GNU Privacy Guard \\
		\url{http://www.gnupg.org}
	\item OpenPGP Message Format \\
		\url{http://www.ietf.org/rfc/rfc2440.txt} 
\end{itemize}

\end{document}